On 2015-10-14 22:19, Devin Asay wrote:
Shouldn’t there be a way to force a string comparison? I know LC tries
to be all helpful about casting numerals as numbers, but what if I
want to know if it’s the exact string?
I think this is one of those things which has come up periodically over
the years...
We added 'is really a' operators in LC8 to help with writing code which
needs to preserve values exactly (the main use-case is lcVCS) - so we
have been considering an 'is really' operator.
(It occurs to me this morning that perhaps these should be 'x really is
a string', or 'x really is y' as opposed to 'x is really a string', or
'x is really y' - I'm not sure which is 'more correct' in English)
The 'is really a' operators check the internal (dynamic type) of the
value, by-passing any type-coercion:
'x is really a string' -> returns true if the current value of x is
(internally) a string
'x is a string' -> returns true if x can be converted to a string
So, the 'is really' operator would do much the same thing:
'x is really y' -> returns true if the internal types of x and y are
the same, and they are the same value
'x is y' -> if x and y can be converted to numbers then compare as
numbers else compare as strings
The problem with 'is really' is that to truly understand what it is
doing, you have to explain about whilst LiveCode is a 'typeless'
language (assuming you ignore the existence of arrays ;)), the engine
still has a notion of distinct types internally (it needs to store the
values in memory in some chosen representation after all) and the
internal type of a value depends on how the value was last produced:
put "0" + 0 into tVar1 -- tVar is really a number
put "0" & 0 into tVar2 -- tVar is really a string
put tVar1 is really tVar2 -- false
The other option (which has the potential advantage of not exposing the
7.0+ under-the-hood dynamically typed nature) is to have an explicit
'compare as string' operator (for purposes of exposition let's call it
is_string) for now. The action of such an operator would be to convert
both sides to strings (if possible) and then compare:
put "0" is_string "0." -- false
put 0+0 is_string char 1 of "0." -- true
This is subtly different from is really:
put 0 + 1 is really "1" -- false
put 0 + 1 is_string "1" -- true
Indeed, if we imagined that we had 'as <type>' operators then:
x is_string y <=> (x as string) is really (y as string)
So, anyway, a couple of potential solutions (I think 'is really' is a
useful compliment to the 'is really a' operators, the question is
whether there is a nice syntax for is_string and whether it is a useful
thing to have).
Warmest Regards,
Mark.
I guess I could do this dance:
if char 1 of fld “display” is “0” and char 2 of fld “display” is NOT
“0” then…
It’s seems to complicated for such a simple thing, especially for
explaining to novice programmers. Maybe I’m missing something obvious.
Devin
Devin Asay
Office of Digital Humanities
Brigham Young University
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Mark Waddingham ~ m...@livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps
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